Tungsten incandescent body containing foreign substances and procedure for its preparation

ABSTRACT

Sintered tungsten filaments for incandescent lamps contain as dopants 0.01-100 ppm beryllium, at least one of 10-100 ppm potassium or 0.1-10 ppm thallium, and at least one of 0.5-2 ppm of alluminum or 0.01-5 ppm gallium. These have greater strength than the corresponding alloys in which silicon is present instead of beryllium. Any silicon in the present invention will be less than half the beryllium by weight.

Elite Sttes atent i 1 Millner et a1.

1 nee.10,1974

[ TUNGSTEN INCANDESCENT BODY CONTAINING FOREIGN SUBSTANCES AND PROCEDUREFOR ITS PREPARATHON [76] Inventors: Tivadar Millner, 108 Mikszat Kalmanu, Budapest 1V; Laszlo Bartha, 76-78 Toldy F. u, Budapest I; JenoNeugebauer, 131, Bocskay u, Budapest XV, all of Hungary [22] Filed: June27, 1972 [21] Appl. No.: 266,578

[30] Foreign Application Priority Data Mar. 16, 1972 Hungary OE 2339[52] U.S. Cl 29/182, 29/1825, 75/176, 75/207, 252/515 [51] Int. Cl. C22cl/05, C22c 22/00 [58] Field of Search 29/1825, 182; 75/207, 75/176;252/515 [56] References Cited UNITED STATES PATENTS 1,602,526 10/1926Gerd ..75/207X Primary Examiner-Benjamin R. Padgett Assistant ExaminerR.E. Schafer Attorney, Agent, or Firm-Young & Thompson [57] ABSTRACTSintered tungsten filaments for incandescent lamps contain as dopants0.01-100 ppm beryllium, at least one of 10-100 ppm potassium or 0.1-l0ppm thallium, and at least one of 0.5-2 ppm of alluminum or 0.01-5 ppmgallium. These have greater strength than the corresponding alloys inwhich silicon is present instead of beryllium. Any silicon in thepresent invention will be less than half the beryllium by weight.

2 Claims, No Drawings TUNGSTEN INCANDESCENT BODY CONTAINING FOREIGNSUBSTANCES AND PROCEDURE FOR ITS PREPARATION The invention relates to atungsten incandescent body containing foreign substances, which is in arecrystallized state, and has high strength at room temperature.

It is known that illuminating tungsten filament incandescent lamps, suchas gas-filled double-coil lamps, halogen-containing incandescent lamps,etc., should be prepared economically out of such tungsten wires fromwhich incandescent bodies which retain their shape at operatingtemperature, that is are not elongated, and which are not brittle atordinary temperatures, may be prepared.

Tungsten wire characteristics corresponding to the requirements ofincandescent lamp production are today generally attained by theaddition of not more than all together one percent of an additivematerial composed of compounds containing K, Si and Al to the basematerial of the tungsten wire: the W or the blue oxide/e.g. WO the thusachieved so called doped base material is then reduced to doped tungstenmetal powder by heating it in a stream of hydrogen. In one form ofpractice the majority of the said additive material is thereafterremoved from such metal powders by washing them out and porous bars arepressed from it. In another practical technique the porous bars arepressed from the doped metal powder without washing it out.

For the purposes of sintering, in both cases the pressed bars are heatedup almost to the melting point. This heating up is achieved by thepassage of an electrical current directly through the bars. In thecourse of this sintering (compacting) in a protective atmosphere ofhydrogen additive materials evaporate out of the bars. The bars preparedby the two practical techniques mentioned are sintered to differentextents, but in such a way that both methods lead to the formation ofsintered rods which can be swaged and drawn into wire, and in which verysmall amounts of foreign materials remain in addition to the tungsten,e.g. foreign materials containing 10-50 ppm K, 1-3 ppm Si and l-2 ppm Alcalculated on the tungsten.

These foreign materials containing a few ppm of K, Si and Al areresponsible for the useful incandescent filament and incandescent bodyproperties: the recrystallization occurring at high temperature andleading to long crystals in the wire, the retention of shape at hightemperature and the not completely satisfactory strength at roomtemperature.

In the following the term additives is applied to those chemicalmaterials which contain (foreign) atom species different from tungstenand which are added to the starting material for the preparation of thetungsten wire. The residual traces of these which are present in theprepared tungsten wire are termed foreign materials, even when theycontain foreign atoms themselves different from tungsten, and when theseconsist of a chemical compound or compounds of the foreign atom speciesdifferent from tungsten.

On the other hand traces of substances or residues of these beingpresent as non-additives but natural impurities, are hereafter calledimpurities.

The aim of the present invention was to improve the strength of tungstenwires in their recrystallized state at normal (room) temperatures. Itwas found that this aim can be achieved by modifying the foreignmaterials hitherto used in tungsten.

As regards the chemical-physical natures of the foreign materials andthe mode of their action, different findings and opinions have beenpresented in the international technical literature.

According to the findings and views associated with the name of RIECK(l), the foreign materials form solid-phase molecules in the tungstenmetal, and give rise to the favourable recrystallization properties,etc., by being situated initially on the surface of the fibres of thedrawn tungsten wires. It is considered possible that the composition ofthe molecules is KAlSi O that is it corresponds to the composition ofthe mineral leucite.

According to the findings associated with the name of WALTER (2), theforeign materials similarly form solid-phase molecules, and give rise tothe recrystallization and other favourable properties by finally beingdispersed throughout the tungsten metal. According to these findings,the molecules have diamaters of about 400 A, while their composition is3Al O .2SiO approximately the same as that of the mineral mullite.

According to more recent observations, a network of spherical microporescan be found in recrystallized tungsten metal doped with foreignmaterials containing K, Si and Al; and according to the most recentobservations these pores contain elemental potassium. According topresent-day views, the network of micropores may give rise to therecrystallization and other favourable properties in tungsten metaldoped with foreign materials containing K, Si and Al in just the sameway as the above-mentioned network of foreign-phase molecules. Thediameters of the spherical micropores are about A.

We do not question the participation of the molecules and bubbles in theformation of the effect of the additive traces, but MILLNER, NEUGEBAUERand KERENYI have already proved that the A1 0 in the trio of additivescontaining K, Si and Al can be replaced by Ga O which is reduced to Gain hydrogen (3), and the K 0 can be replaced by T1 0 which is reduced toT1 in hydrogen (4), without impairing the good recrystallization andother properties. This supports the idea that the effect of the foreignmaterials and additives containing K, Si and Al is by no means basedonly on the effect of the foreign-phase molecules: a dominant orequivalent role in this effect may also be played by K and Al atoms too,for example.

In addition to this, as long ago as 1931 MILLNER and TURY (5) describedthat the foreign materials can exert a considerable vapour pressure inthe bars during sintering and in the wire during recrystallization; thisvapour pressure produces an internal stress state in the metal body andhence leads to the formation of large crystals. The more recent theoryof the network of spherical micropores is in agreement with thissuggestion and demonstrates the role of the K atoms from among theforeign materials.

When our knowledge of the mode of action of the foreign materials wasthus enlarged, but a complete agreement could still not be attained, weconsidered the question of whether the SiO in the trio of additivescontaining K, Si and Al could also be replaced by some analogous oxidewhich can be reduced with hydrogen without impairing the good propertiesof the metal.

These studies, which extended to GeO among others, have so far not ledto a result.

This directed our attention to the fact that while, as we have seen, thegood effect is exerted by Tl atoms instead of K in the trio of additivescontaining K, Si and Al, and the same is done by Ga atoms instead of Al-O in the case of SiO it may be possible that it is not Si or analogousatoms which are responsible for the effects, but rather somecharacteristic silicon-oxygen bonding. This means that as regards theSiO additive we should not look for a substitute with an analogousfavourable effect among the atoms similar to Si, but should try to findit among those atoms which behave similarly to Si in their bonding tooxygen.

Geochemical and mineralogical considerations led us to the fact that innature (in the mineral world) Be atoms for example behave similarlytowards oxygen as do Si atoms. The bonding of Si atoms to oxygen ischaracterized by the fact that in minerals Si is coordinated to oxygenpractically without exception in tetrahedra, and thus SiO tetrahedra arepresent. Be atoms in minerals behave exactly similarly: in almost allBecontaining minerals BeO, tetrahedra occur.

It is considered favourable that the radius of the Be ion, 0.34 A, iseven smaller than that of the Si ion, 0.39 A, and that the strength ofthe Be-0 bond, ca. 75Kcal/mole, is much higher that that of the Si0bond, ca. 51 Kcal/mole. A tungsten metal powder was therefore preparedby the addition of an aqueous solution of KCl, BeCl and Al Cl to the W0base material, with the aim of examining whether, by replacing the SiOwith BeO which is even more difficult to reduce with hydrogen, thelarge-crystalline structure would remain and other properties betterthan those already known would appear.

The additive-containing aqueous paste was dried, the doped W0 wasreduced with hydrogen, a bar was pressed from the metal powder formed,and this was then sintered by the passage of an electric current. Thesintered bar was worked into incandescent lamp wires by swaging andwire-drawing. It was observed that the recrystallization,form-retaining, strength and other useful properties of the wires soprepared containing K, Be and Al foreign materials, that is theberyllium tungsten wires prepared in accordance with the invention, inpractice did not fall behind the corresponding properties of the knownwires containing K, Si and Al foreign materials, while in addition theirstrength in the recrystallied state was substantially better at normal(room) temperatures than that of the doped wires containing K, Si and A]foreign materials. In our opinion, the reason for this is to be found inthe fact that the -WOBe-OW-bonding of the crystallite boundaries isstronger than the --W-OSi- -O-Wbonding.

It must be mentioned that the favourable effects of the foreignmaterials and additives containing beryllium were found by experience,and the assertion of the effects does not depend on the validity of theexplanations attributed to them.

The tungsten wires prepared according to the invention, and thustungsten wires prepared with additive materials containing K, Be, Al orTl, Be, Ga or K, Be or K, Be, Al, Ga etc., for example, do not containconsiderable amounts (either as impurities or as foreign materials) ofSi or compounds containing Si, but do contain, and precisely instead ofit, foreign material containing Be; in this way the wires differprimarily from the tungsten wires prepared with the foreign materials BeSiO or BeSiO according to the British Pat.

No. 258,642 published in 1926 (6). According to the description in thisBritish Pat. No. 258,642, as a result of the beryllium silicate foreignmaterials these wires are free of the off-set phenomenon which can occurat the temperature of the incandescent filament. It is generally knownthat this detrimental phenomenon occurs when those crystallites of therecrystallized tungsten wires which are in contact with the boundarieslargely normal to the axis of the wire gradually slip on each other onthese boundaries, whereby the conductor cross-section decreases locallyand hence the incandescent filament burns out prematurely (7). Theoff-set phenomenon was a characteristic fault of tungsten wires preparedaccording to the old practice and containing much impurity, e.g. muchcalcium oxide, etc. Nowhere in the description in the British Pat. No.258,642 is it asserted that the recrystallized beryllium silicatetungsten wires are not brittle at ordinary temperatures or that they aresignificantly stronger than for example the so-called pure, that isadditve-free, tungsten wires.

Our invention does not extend to the use of beryllium silicate as anadditive or a foreign material, because experience showed that thestrength-increasing effect of BeO observed by us is completely marred bythe necessary SiO content, presumably for the very reason that it leadsto the formation of beryllium silicates, when the Be is bound by thefavourable oxygen bonds mentioned above, however, not towards the Watoms, but towards the Si atoms.

It was observed during our experiments that in order to attain thefavourable effect of the berylliumcontaining foreign materials it wasnecessary for the beryllium content of the tungsten wire according tothe invention to be at least 0.000001 percent, that is 0.01 ppm. It wasalso observed that to avoid the disturbing effect of silicon-containingforeign material or impurity traces and thus for the necessaryattainment of the favourable effect of the beryllium-containingsiliconfree additive, it was sufficient if the silicon content of thetungsten wires according to the invention was less than half theberyllium content so as to ensure a considerable beryllium content beingindependent from the Si content.

Our invention is thus a foreign material-containing tungstenincandescent body, which is in a recrystallized state, has high strengthat room temperature, and is characterized by the facts that one of theforeign materials contains beryllium, that the beryllium content of thetungsten incandescent body is 0.01-100 ppm, and that the silicon content(impurity) is less than half the beryllium content.

The procedure for the preparation of the tungsten incandescent bodyaccording to the invention is characterized by the fact that asilicon-free beryllium compound is added as one of the additives, in aproportion of 100l0,000 ppm calculated as beryllium oxide, to a tungstenoxide the silicon dioxide impurity of which does not exceed the amountcorresponding to the atomic ratio one silicon to six berylliums, and thetungsten oxide is itself then reduced to metal powder, pressed, sinteredand swaged, and finally formed into wire by wire-drawing and hence intoan incandescent body, by known methods.

The preparation of the tungsten incandescent body according to theinvention can also be carried out in such a way that the silicon dioxideimpurity content is adjusted to less than the amount corresponding tothe atomic ratio one silicon to six berylliums by the washing out of thereduced metal powder or the partially sintered metal body, for exampleby the washing out with a hydrofluoric acid solution by a known method.

According to the composition given for the tungsten incandescent body inaccordance with the invention, a maximum of about one-sixth part of theberyllium content in the incandescent body may be bound by the silicon.It follows from the atomic weights of beryllium and silicon that for90.2 parts by weight of beryllium to form beryllium silicate ofcomposition BeSiO in its complete entirety, 280.6 parts by weight ofsilicon are necessary. Thus, 45 .1 parts by weight of silicon, i.e. halfof 90.2 parts by weight, bind 45.1 /280.6, i.e. approximately one-sixthpart of 90.2 parts by weight of the beryllium amount.

By the terms tungsten wire and tungsten incandescent body according tothe invention are understood a tungsten wire and a tungsten incandescentbody which in addition to the proposed Be-containing foreign materialsalso contain one or more other foreign materials, such as for exampleforeign materials containing K and- /or Al, or K and or Ga, as well asfor example Tl and/or A, or Tl and/or Ga, etc., but does not containsilicon only as an impurity (if it does).

In this respect we have to remark that due to the fact that the foreignmaterials present in tungsten are partly present in atomic form, partlyin some compounds (as added or formed during working of the rawmaterial) further because according to the literature this question isnot clarified, we shall speak about foreign materials independentlywether they are present in atomic state or in some compound and shallexpress the amount of the traces of these foreign materials in thereduced tungsten material uniformally always in their atomic state.

We have found that in all the additive material trio combinations so farstudied, which also contain SiO and give rise to large-crystalline,useful incandescent filament properties in the tungsten wires, such afor example in the additive combinations containing K, Si, Ga or K, Si,Al or Tl, Si, Al or Tl, Si, Ga, the foreign material containing the Si0can be favourably exchanged for foreign material containing BeO, becauseby this means among other results the roomtemperature strength of thetungsten incandescent bodies is increased significantly, without theappreciable decrease of their other good properties.

To data tungsten wires have been prepared for use as incandescent lamps,which have properties considered as satisfactory as a result of foreignmaterial containing not two, but one or more than two different elementsin addition to the SiO -containing foreign material. We have found thatin the foreign material combinations studied to date and applied in thepreparation of such wires too the foreign material containing SiO can befavourably exchanged for the foreign material containing BeO.

Tungsten wires prepared with the combination of two foreign materialscontaining for example K and Be according to the invention and in theirrecrystallized state attain the average good properties and thestructure consisting of average sized crystals of known tungsten wiresprepared with foreign materials containing K and Si. In addition tothis, however, their strength in the recrystallized state at ordinarytemperatures is substantially better than such strength of wiresprepared with foreign materials containing K and Si.

Tungsten wires prepared with the foreign material quartet combinationcontaining for example K, Be, Al and Ga according to the invention arelarge-crystalline on recrystallization, and their good properties attainand even exceed the good properties of known tungsten wires preparedwith the foreign material trio combination containing K, Si and Al; inaddition to this their strength in the recrystallized state at roomtemperature is substantially better than such strength of knownrecrystallized tungsten wires prepared with the foreign material trio K,Si and Al.

By the use of foreign materials containing beryllium, tungstenincandescent bodies with many types of favourable properties can beprepared, as is clear from the following reported examples and theiraccompanying description.

EXAMPLE 1 A 0.3% aqueous solution of KCl, an aqueous solution ofberyllium chloride corresponding to 0.20% BeO, and an aqueous solutionof aluminum chloride corresponding to 0.05% A1 0 calculated with respectto the W0 are added to a dilute aqueous paste of W0 powder prepared byheating from ammonium paratungstate (the so-called para-crystals), andthen tungsten metal powder is made from this in the normal way, that isby drying and by reduction with hydrogen. Bars are pressed from themetal powder, and these are sintered to make them compact by heatingthem with an electric current in hydrogen gas. The bars thus preparedcontain approximately O.10-10.0 ppm Be, 1-2 ppm Al and 10-100 ppm K.

EXAMPLE 2 An aqueous solution of thallium/l/nitrate corresponding to0.1% T1, an aqueous solution of beryllium chloride corresponding to0.20% BeO and an aqueous solution of aluminum chloride corresponding to0.05% A1 0 calculated with respect to the W0 are added to a diluteaqueous paste of blue oxide powder of composition W0 prepared frompara-crystals by heating and mild reduction, and then from this by themethod of Example 1 compact, sintered tungsten bars are prepared. Suchbars contain approximately 0.10-10.0 ppm Be, 1-2 ppm Aland 0.0110.0 ppmTl.

EXAMPLE 3 A 0.3% aquoeus solution of KCl, an aqueous solution ofberyllium nitrate corresponding to 0.20% BeO and an aqueous solution ofgallium nitrate corresponding to 0.03% Ga O calculated with respect tothe W0 are added to a dilute aqueous paste of blue oxide" powder ofcomposition W0 obtained from para-crystals by heating and mildreduction, and then from this by the method of Example 1 compact,sintered tungsten bars are prepared. Bars so prepared containapproximately 0. l0-10.0 ppm Be, 0.01-5 ppm Ga and 10-100 ppm K.

EXAMPLE 4 An aqueous solution of thallium/l/nitrate corresponding to0.1% Tl, an aqueous solution of beryllium nitrate corresponding to 0.20%BeO and an aqueous solution of gallium nitrate corresponding to 0.03% GaO calculated with respect to the W are added to a dilute aqueous pasteof W0 powder prepared from para-crystals by heating, and then from thisby the method of Example 1 compact, sintered tungsten bars are prepared.Bars so prepared contain approximately 010-100 ppm Be, 0.0l ppm Ga and01-100 ppm Tl.

' EXAMPLE 6 A 0.3% aqueous solution of KCl, an aqueous solution ofberyllium nitrate corresponding to 0.02% BeO and an aqueous solution ofaluminum chloride corresponding to 0.05% A1 0 calculated with respect tothe W0 are added to a dilute aqueous paste of W0 powder prepared frompara-crystals by heating, and then from this by the procedure of Example1 compact, sintered tungsten bars are prepared. Bars so prepared containapproximately 0.0l-l.0 ppm Be, 1-2 ppm Al and l00 ppm K.

EXAMPLE 6 EXAMPLE 7 A 0.3 aqueous solution of KCl, an aqueous solutionof beryllium chloride corresponding to 0.02% BeO and an aqueous solutionof gallium nitrate corresponding to 0.03% Ga O calculated with respectto the W0 are added to a dilute aqueous paste of blue oxide powder ofcomposition W0 prepared from paracrystals by heating and mild reduction,and then from this by the procedure of Example 1 compact, sinteredtungsten bars are prepared. Bars so prepared contain approximately0.0ll.0 ppm Be, 0.01-5 ppm Ga and 10-50 ppm K.

EXAMPLE 8 An aqueous solution of thallium/I/nitrate corresponding to0.1% Tl, an aqueous solution of beryllium nitrate corresponding to 0.02%BeO and an aqueous solution of gallium nitrate corresponding to 0.03% GaO calculated with respect to the W0 are added to a dilute aqueous pasteof WO .l-l O precipitated with boiling hydrochloric acid from a boilingaqueous solution of Na WO and then from this by the method of example 1compact, sintered tungsten bars are prepared. Bars so prepared containapproximately 0.0ll.0 ppm Be, 0.0l-1.0 ppm Ga and 0.1-1.0 ppm EXAMPLE 9A 0.3% aqueous solution of KCl, an aqueous solution of BeClcorresponding to 0.02% BeO, an aqueous solution of Al Cl correspondingto 0.03% A1 0 and an aqueous solution of gallium nitrate correspondingto 0.03% Ga O calculated with respect to the W0 are added to a diluteaqueous paste of blue oxide powder of composition W0 prepared frompara-crystals by heating and mild reduction, and then from this by theprocedure of Example 1 compact, sintered tungsten bars are prepared.Bars so prepared contain approximately 0.0l-l.0 ppm beryllium, 0.5-1.0ppm aluminium, 0.0l5.0 ppm gallium and l050 ppm potassium.

Beryllium tungsten bars prepared according to Examples l to 8 and 9 areswaged and worked into drawn wire, and from this coil-shapedincandescent bodies with a wire diameter of 0.3 mm for example, and also220 V/40 W double coils with a wire diameter of 0.014 mm are prepared;it is observed that in these on recrystallization a structure developswhich consists of crystals much longer than the wire diameter. The otherproperties of such beryllium tungsten incandescent bodies in generalattain the good properties of silicon tungsten incandescent bodiesprepared with foreign materials containing K, Si and Al. Theroomtemperature strength of the recrystallized beryllium tungstenincandescent bodies, however, far exceeds those of recrystallizedsilicon tungsten incandescent bodies: while 220 V/40 W recrystallizeddouble coils prepared with foreign materials containing K, Si and Al canbe drawn out to about twice their original length at room temperaturewithout breaking, the beryllium tungsten recrystallized 220 V/40 Wdouble coils can be drawn out on average to three-four times theiroriginal length.

Incandescent bodies, for example 220 V/40 W double coils, can beprepared from the beryllium tungsten bars made with foreign materialcontaining Tl, but without foreign material containing K, as in Examples2, 4, 6 and 8, such that they do not burn out by arcing in gas-filledincandescent lamps among others corresponding to the description in theHungarian Pat. No. 155,352 (4), not even if they are connected in thefirst instance directly at the maximum incandescent filamenttemperature, which causes burn out by arcing almost without exception inthe case of incandescent filaments prepared with foreign materialscontaining K, Si, and Al. Foreign material containing Be does not marthe favourable effect of foreign material containing Tl.

The wires of beryllium tungsten bars prepared according to Examples 6and 8 are particularly suitable for incandescent bodies of incandescentlamps containing halogen, in which in addition to a crystal structureensuring retention of shape it is also desirable (in order to ensure thenon-disturbance of the gas-space processes) to maintain the possiblyevaporating foreign material content of the incandescent filaments at enextremely low level.

REFERENCES Specification No. 106,268 (1931).

6. THE EDISON SWAN ELECTRIC COMPANY.

Ltd., and PERCIVAL, G. A.: British Patent Specification No. 258,642(1926).

7. SMlTl-IELLS, G. J.: Tungsten, p. 91 (1926).

What we claim is:

1. A sintered tungsten incandescent body containing 0.01- ppm beryllium,at least one member selected from the group consisting of 10-100 ppmpotassium and 0.1-10 ppm thallium, and at least one member selected fromthe group consisting of O.52 ppm of aluminum and 0.01-5 ppm gallium,containing less than half as much silicon as beryllium by weight,balance essentially tungsten.

2. A sintered tungsten product as claimed in claim 1, in which saidberyllium is present in the amount of 0.1010ppm.

1. A SINTERED TUNGSTEN INCADESCENT BODY CONTAINING 0.01 - 100 PPMBERYLLIUM, AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF10-100 PPM POTASSIUM AND 0.1-10 PPM THALLIUM, AND AT LEAST ONE MEMBERSELECTED FROM THE GROUP CONSISTING OF 0.5-2 PPM OF ALUMINUM AND 0.01-5PPM GALLIUM, CONTAINING LESS THAN HALF AS MUCH SILICON AS BERYLLIUM BYWEIGHT, BALANCE ESSENTIALLY TUNGSTEN.
 2. A sintered tungsten product asclaimed in claim 1, in which said beryllium is present in the amount of0.10-10ppm.